Organ, cell and tissue transplant rejection and the various autoimmune diseases are thought to be primarily the result of a T-cell mediated immune response. This T-cell mediated immune response is initially triggered by helper T-cells which are capable of recognizing specific antigens. These helper T-cells may be memory cells left over from a previous immune response or naive cells which are released by the thymus and may express any of an extremely wide variety of antigen receptors. When one of these helper T-cells recognizes an antigen present on the surface of an antigen presenting cell (APC) or a macrophage in the form of an antigen-MHC complex, the helper T-cell is stimulated to produce IL-2 by signals emanating from the antigen-specific T-cell receptor, co-receptors, and IL-1 secreted by the APC or macrophage. The helper T-cells then proliferate. Proliferation results in a large population of T-cells which are clonally selected to recognize a particular antigen. T-cell activation may also stimulate B-cell activation and nonspecific macrophage responses.
Some of these proliferating cells differentiate into cytotoxic T-cells which destroy cells having the selected antigen. After the antigen is no longer present, the mature clonally selected cells will remain as memory helper and memory cytotoxic T-cells, which will circulate in the body and recognize the antigen should it show up again. If the antigen triggering this response is not a foreign antigen, but a self antigen, the result is autoimmune disease; if the antigen is an antigen from a transplanted organ, the result is graft rejection. Consequently, it is desirable to be able to regulate this T-cell mediated immune response.
CD45 antigen (CD45) is expressed on most leukocytes. Indeed, it was previously thought that a common CD45 antigen was present on all leukocytes, for which reason the receptor was originally known as the Leukocyte Common Antigen (LCA). Monoclonal antibodies (mAbs) to CD45 were proposed as a means of effectively eliminating all leukocytes where desirable, for example, purging an organ to be transplanted of passenger leukocytes prior to transplantation using nonspecific CD45 monoclonal antibody. See, e.g.,WO 91/05568.
It has recently been shown that different isoforms of CD45 are generated by alternate splicing of a single primary transcript of the CD45 gene. These CD45 isoforms include CD45RA, CD45RB, CD45RC, and CD45RO. CD45RA contains the expression product of exon 4 (sometimes referred to as RA) of the CD45 gene; CD45C contains the expression product of exon 6; CD45RB contains the expression product of exon 5; CD45RO does not contain the expression products of any of the three exons 4, 5, or 6. See Hall et al, xe2x80x9cComplete Exon-Intron Organization of the Human Leukocyte Common Antigen (CD45) Gene,xe2x80x9d J. Immunol., 141, 2781 (1988), herein incorporated by reference and Streuli et al, xe2x80x9cCharacterization of CD45 and CD45R Monoclonal Antibodies Using Transfected Mouse Cell Lines that Express Individual Human Leukocyte Common Antigens,xe2x80x9d J. Immunol., 141, 3910 (1988). The significance of this variable expression, however, has been unclear.
Increased success in clinical organ transplantation has paralleled improvements in techniques for immunosuppression. However, increasingly potent immunosuppressant drugs often produce complications due to their lack of specificity. For example, recipients can become very susceptible to infection. Highly specific immunosuppression is therefore desired.
The ideal specific immunosuppression method would be a treatment which suppresses the action of the lymphocytes responsible for rejection of the particular graft the patient receives without otherwise affecting the immune system.
Therefore, a need exists to durably and selectively suppress or otherwise modulate the immune response in humans, particularly transplant recipients or those afflicted with autoimmune diseases.
The present invention provides a method for in vivo immunosuppression in humans and mammals. The methods include pretreatment in vivo therapies to prevent rejection of transplanted cells, tissues and organs and post-transplant in vivo therapies to reverse a pathological immune response. Preferably, the present method can impart durable tolerance, rather than just delayed rejection to the recipient. The methods also include in vivo treatment of autoimmune diseases.
Specifically, the method of the present invention comprises administering to a patient in need of such treatment, an effective immunosuppressive amount of at least one compound which binds specifically to a CD45 leukocyte antigen present on T-cells. For example, the method of the present invention can be used to treat a patient undergoing transplant rejection, including graft-versus host disease or afflicted with an autoimmune disease. Preferably, the compound binds to the CD45RB receptor. The present invention additionally provides pharmaceutical compositions comprising an effective immunosuppressive amount of at least one compound which specifically binds to a CD45 antigen in combination with a pharmaceutically acceptable carrier. The term xe2x80x9ccompoundxe2x80x9d is meant to indicate, for example, antibodies as defined herein, and molecules having antibody-like function such as synthetic analogues of antibodies, e.g., single-chain antigen binding molecules, small binding peptides, or mixtures thereof.
Preferably, the compound of the present method is an antibody. More preferably, the antibody administered will be capable of binding to the CD45RB leukocyte antigen, the CD45RO leukocyte antigen, the CD45RA leukocyte antigen or the CD45RC leukocyte antigen. Most preferably, the antibody is capable of binding to the CD45RB or CD45RO leukocyte antigen.
As mentioned hereinabove, the method of the present invention is useful in the treatment of transplant rejection. More specifically, the method may be employed for the treatment of a patient that has undergone cell tissue or organ transplantation that is either allogeneic or xenogeneic. Furthermore, the method of the present invention may be utilized prior to, following or concurrently with the transplant procedure, or any combination thereof.
The method of the present invention is contemplated to be beneficial in a variety of transplant situations, even those situations where a recipient may receive sequential transplants of the same or different cells, tissues, or organs. For example, the method of the present invention may be utilized during a heart, liver, bone marrow or kidney transplant, or during the transplantation of pancreatic islets or vascular tissue, e.g., a coronary bypass procedure.
The method of the present invention may also be useful in the treatment or prevention of autoimmune disease, inflammatory conditions and arthritic or rheumatoid diseases. For example, the method of the present invention may be employed for the treatment of autoimmune hematological disorders, systemic lupus erythematosus, inflammatory bowel disease, ulcerative colitis, Crohn""s disease, multiple sclerosis, diabetes mellitus type 1, and the like.
In a further embodiment of the method of the present invention, an anti-inflammatory or immunosuppressive drug may be administered prior to, following, or concurrently with the compound described hereinabove. For example, suitable drugs for this purpose include, but are not limited to, cyclosporin, FK-506, rapamycin, corticosteroids, cyclophosphamide, mycophenolate, mofetil, leflunomide, anti-lymphocyte globulins, deoxyspergualin OKT-3 and the like.
In yet another embodiment, the method of the present invention may further comprise administering an amount of the patient""s lymphocytes to the patient, i.e., in combination with the CD45 leukocyte antigen binding compound(s).
This invention is based on the discovery that leukocytes such as different types of T lymphocytes, or xe2x80x9cT-cellsxe2x80x9d may predominantly express one or another CD45 isoform. Naive helper T-cells and memory T-cells express predominately CD45RA and CD45RO respectively. CD 45RB expression is also variable; it is highly expressed (bright) on naive helper T-cells (Th0) and on T-cells that produce predominantly interleukin 2 and can induce inflammatory and cytotoxic responses (Th1). T cells that predominantly produce interleukin 4 and induce humoral immune responses (Th2) have low CD45RB expression (dim).
It has now been shown that some antibodies which react with CD45RB (MB23G2 in mouse, 6G3 in primates) are capable of selectively inhibiting the inflammatory and cytotoxic T-cell mediated immune response without destroying the pool of memory T-cells. Consequently, CD45RB suppressors have a great advantage over current immunosuppressants in that (i) they act on a particular T-cell population rather than having an overall immunosuppressive effect, thereby avoiding the risk of side effects associated with over-suppression of the immune system; and (ii) they are capable of conferring long term tolerance to a particular antigen when they are administered contemporaneously with exposure to antigen, e.g., just before and after an organ transplant or during an acute phase of an autoimmune disease.
As used herein, the term xe2x80x9cimmune tolerancexe2x80x9d or simply xe2x80x9ctolerancexe2x80x9d is intended to refer to the durable active state of unresponsiveness by lymphoid cells to a preselected or specific antigen or set of antigens. The immune response to other immunogens is thus unaffected, while the requirement for sustained exogenous immunotherapy is either reduced or is eliminated. Additionally, tolerance enables subsequent transplantation of material comprising the same antigen or set of antigens without increasing the need for exogenous immunotherapy.
Generally, it is believed that the present methods may lead to T-cells having a receptor for the antigen becoming anergized, so that the T-cell clones are functionally, if not actually, deleted. For a fully functional activation of T-cells two signals are necessary. The first signal requires recognition of an antigen via the T-cell receptor. The second signal requires interaction between co-stimulatory molecules, such as B7, on antigen presenting cells and receptors, such as CD28, on the T-cells. It is generally accepted that lack of this second signal through CD28 leads to anergy. However, CD45 is required for the activation through the T-cell receptor and interference with this process through CD45RB interrupts the first signal and can also lead to anergy. This is in fact a more fundamental approach than blocking of the B7-CD28 interaction, since there are a number of different co-stimulatory pathways, whereas there is only the one T-cell receptor complex. Since CD45 is differentially expressed it is also possible to selectively affect specific subsets of T-cells. Thus, the observed effects are not due solely to depletion of a subset, or of the general T-cell population, but rather involve a combination of transitory depletion and a durable effect that leads to tolerization of the recipients. For example, in a mouse kidney transplant model, allograft tolerance following initial treatment with anti-CD45RB monoclonal antibody persists indefinitely, with survival well in excess of 100 days. In mice surviving over 100 days following a kidney allograft, the present method permits skin grafts syngeneic with the donor kidney to be tolerated, while skin grafts allogeneic with both the recipient and the donor kidney were rejected.
The term xe2x80x9cantibodyxe2x80x9d, includes human and animal mAbs, and preparations of polyclonal antibodies, as well as antibody fragments, synthetic antibodies, including recombinant antibodies, chimeric antibodies, including humanized antibodies, anti-idiotopic antibodies and derivatives thereof.
As used herein, the term xe2x80x9ctreatingxe2x80x9d, with respect to an autoimmune disease or condition includes preventing the onset or flare-up of the disease or condition, as well as reducing or eliminating one or more symptoms of the disease or condition.